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kareinaThanks to a chat with my advisor this afternoon, I may have stumbled upon the first use of the term "mylonite" in a geologic publication. If not the very first, certainly an early one! He had commented that part of the reason I need to include some cross-sections of my field area in my thesis is because the last time anyone published such a thing for this area was in the 1960's before anyone knew about mylonites and what they tell us about the deformation of an area.
This got me to wondering about just *when* they learned about mylonites, and rather than ask my advisor, I checked on Scopus for papers published on the topic between 1960 and 1970. There was one, published in Nature in 1967. Alas, UTAS doesn't have a subscription to the on-line version of that journal, so it was necessary to walk all the way down to the library and get the paper copy and make a photocopy of it. Looking at that article, I noticed early on it in a reference to "Lapworth's definition" of mylonite, and saw that the list of references included a 1885 article by Charles Lapworth. So I checked, and sure enough, UTAS happens to have this journal going back that far! (It is so cool to handle the actually journal from that long ago!)
Therefore, for your reading pleasure, I typed up the article, with the relevant definitions in bold print.
The Highland Controversy in British Geology: its Causes, Course, and Consequences, by Chas. Lapworth, LL.D, F.G.S, Professor of Geology and Physiography, Mason College, Birmingham.
The author gave a résumé of the views of the earlier geologists respecting the geological age and possible mode of formation of the Highland metamorphic rocks; and sketched, in brief, the rise and progress of the controversy between Sir Rod. Murchison and his followers on the one hand, and Prof. Nicol, of Aberdeen, on the other, till its temporary close in 1861, by the publication of the Highland Memoir of Murchison and Geikie. The then reviewed the reopening of the controversy by Dr. Hicks in 1878, and the work of the Archaean geologists, up to the date of publication of Dr. C. Callaway’s paper in 1883, in which Nicol’s view of the great physical break between the Palaeozoic rocks and the Eastern or Upper Gneissic series was shown to be correct, but the so-called Eastern gneiss was provisionally erected into a new Archaean system, the Caledonian, having the Arnaboll gneiss as its lower member. The author next gave a summary of his own views as deduced from his personal study of the Durness Eriboll district in 1882 and 1883, and published in 1884, illustrating these by coloured maps and sections. He held that (exception being made of the local Torridon Sandstone) the only rock-formations in the Durness-Eriboll area are, as Nicol originally contended: (I) The Archæan or Hebridean gneiss; and (2) The Palaeozoic quartzites, fucoid beds, and limestones. But the so-called upper gneiss or eastern metamorphic gneiss appears to be composed of elements derived from one or other of the foregoing. There is no conformable ascending succession from the Palaeozoic rocks into this Eastern Metamorphic series. The line of contact is, generally speaking, a plane of dislocation, and where this is wanting the Palæozoic rocks rest unconformably upon one of the members of the eastern gneiss. The present physical relations of the eastern metamorphic series are the effect of lateral curst creep, by which the eastern metamorphic rocks have been forced over the Palaeozoic rocks in the grand overfaults to the west, often for many miles. This Eastern Metamorphic series is composed of two petrological members, the Arnaboll gneiss to the west, and the Sutherland schists and gneisses to the east, having between them a series of variegated schists possessing characters common to both. The Arnaboll gneiss is simply the easterly extension of the Hebridean of the west. The remaining gneisses and schists of the eastern metamorphic series are mainly composed of remetamorphosed Hebridean, with included patches of igneous and Palaeozoic material. The planes of schistosity which divide the layers of the Upper Gneissic series are not planes of bedding, but planes of dislocation. The dip and strike of these planes have been given to them since Silurian times by the agency of the great earth-movements. In some instance the original structures of the rocks are still recognisable; usually, however, they are wholly obliterated: the old minerals have disappeared as such, and new minerals have been developed, The Eastern Gneissic series has thus no pretension whatever to the title of a sedimentary rock-system. It is a petrological rock-massif, a metamorphic compound, composed of local elements of very different geological ages. In all their essentials these views appear to agree with the farm ore contended and minute results worked out independently, and published by Messrs, Peach and Horne in November 1884.
In the second part of his paper the author gave a summary of the work accomplished among the metamorphic rocks of the Alps and Eastern Germany by Heim and Lehmann; and described the several types of rock-metamorphism found in the Eriboll district, as worked out by himself. The Arnaboll (Hebridean gneiss) can be traced stage by stage from spots where it retains its original strike and petrological characters, to others where it acquires the normal strike and mineralogical features of the ordinary Sutherland schists. The old planes of schistosity become obliterated, and new ones are developed; the original crystals are crushed and spread out, and new secondary minerals, mica and quartz, are developed. The most intense mechanical metamorphism occurs along the grand dislocation (thrust) planes, where the gneisses and pegmatites resting on those planes are crushed, dragged, and ground out into a finely-laminated schist (Mylonite, Gr. mylon, a mill) composed of shattered fragments of the original crystals of the rock set in a cement of secondary quartz, the lamination being defined by minute inosculating lines (fluxion lines) of kaolin or chlorite material and secondary crystals of mica. Whatever rock rests immediately upon the thrust-plane, whether Archæan, igneous, or Palæozoic &c., is similarly treated, the resulting mylonite varying in colour and composition according to the material from which it is formed. The variegated schists which form the transitional zones between the Arnaboll gneiss and Sutherland mica-schists are all essentially mylonites in origin and structure, and appear to have been formed along many dislocation planes, some of which still show between the patches of recognisable Archæan and Palæozoic rocks. These variegated schists (Phyllites or Mylonites) differ locally in composition according to the material from which they have been derived, and in petrological character according to the special physical accidents to which they have been subjected since their date of origin—forming frilled schists, veined schists, glazed schists, &c., &c. The more highly crystalline flaggy mica-schists, &c., which lie generally to the east of the zones of the variegated schists, appear to have been made out of similar material to those of the variegated schists, but to have been formed under somewhat different conditions. They show the fluxion-structure of the mylonites; but the differential motion of the component particles seems to have been the less, while the chemical change was much greater. In some of these crystalline schists (the augen-schists) the larger crystals of the original rock from which the schist was formed, are still individually recognisable, while the new matrix containing them is a secondary crystalline matrix of quartz and mica arranged in the fluxion-planes. While the mylonites may be described as microscopic pressure-breccias with fluxion-structure, in which the interstitial dusty, siliceous, and kaolinitic paste has only crystallized in part; the augen-schists are pressure-breccias, with fluxion-structure in which the whole of the interstitial paste as crystallised out. The mylonites were formed along the thrust-planes, where the two superposed rock-systems moved over each others as solid masses; the augen-schists were probably formed in the more central parts of the moving system, where the all-surrounding weight and pressure forced the rock to yield somewhat like a plastic body. Between these augen-schists there appears to be every gradation, on the one hand, to the mylonites, and on the other to the typical mica-schists composed of quartz and mica. Like the mylonites, the crystalline augenites and micalites present us with local differences in chemical composition (calcareous, hornblendic, quartzose, &c.), suggestive of Archæan, igneous, or Palaeozoic origin. They also show similar structural varieties due to secondary physical changes (frilled, veined, glazed, &c.), as well as others due to the presence of special minerals (garnet, actinolite, &c., &c.).
(yes, I am silly enough to spend the time to type it up, both(!) paragraphs from the photocopy!) I found it odd that the paper describes what the author said, rather than simply saying it, but perhaps this is a summary of a presentation he gave somewhere?
This got me to wondering about just *when* they learned about mylonites, and rather than ask my advisor, I checked on Scopus for papers published on the topic between 1960 and 1970. There was one, published in Nature in 1967. Alas, UTAS doesn't have a subscription to the on-line version of that journal, so it was necessary to walk all the way down to the library and get the paper copy and make a photocopy of it. Looking at that article, I noticed early on it in a reference to "Lapworth's definition" of mylonite, and saw that the list of references included a 1885 article by Charles Lapworth. So I checked, and sure enough, UTAS happens to have this journal going back that far! (It is so cool to handle the actually journal from that long ago!)
Therefore, for your reading pleasure, I typed up the article, with the relevant definitions in bold print.
The Highland Controversy in British Geology: its Causes, Course, and Consequences, by Chas. Lapworth, LL.D, F.G.S, Professor of Geology and Physiography, Mason College, Birmingham.
The author gave a résumé of the views of the earlier geologists respecting the geological age and possible mode of formation of the Highland metamorphic rocks; and sketched, in brief, the rise and progress of the controversy between Sir Rod. Murchison and his followers on the one hand, and Prof. Nicol, of Aberdeen, on the other, till its temporary close in 1861, by the publication of the Highland Memoir of Murchison and Geikie. The then reviewed the reopening of the controversy by Dr. Hicks in 1878, and the work of the Archaean geologists, up to the date of publication of Dr. C. Callaway’s paper in 1883, in which Nicol’s view of the great physical break between the Palaeozoic rocks and the Eastern or Upper Gneissic series was shown to be correct, but the so-called Eastern gneiss was provisionally erected into a new Archaean system, the Caledonian, having the Arnaboll gneiss as its lower member. The author next gave a summary of his own views as deduced from his personal study of the Durness Eriboll district in 1882 and 1883, and published in 1884, illustrating these by coloured maps and sections. He held that (exception being made of the local Torridon Sandstone) the only rock-formations in the Durness-Eriboll area are, as Nicol originally contended: (I) The Archæan or Hebridean gneiss; and (2) The Palaeozoic quartzites, fucoid beds, and limestones. But the so-called upper gneiss or eastern metamorphic gneiss appears to be composed of elements derived from one or other of the foregoing. There is no conformable ascending succession from the Palaeozoic rocks into this Eastern Metamorphic series. The line of contact is, generally speaking, a plane of dislocation, and where this is wanting the Palæozoic rocks rest unconformably upon one of the members of the eastern gneiss. The present physical relations of the eastern metamorphic series are the effect of lateral curst creep, by which the eastern metamorphic rocks have been forced over the Palaeozoic rocks in the grand overfaults to the west, often for many miles. This Eastern Metamorphic series is composed of two petrological members, the Arnaboll gneiss to the west, and the Sutherland schists and gneisses to the east, having between them a series of variegated schists possessing characters common to both. The Arnaboll gneiss is simply the easterly extension of the Hebridean of the west. The remaining gneisses and schists of the eastern metamorphic series are mainly composed of remetamorphosed Hebridean, with included patches of igneous and Palaeozoic material. The planes of schistosity which divide the layers of the Upper Gneissic series are not planes of bedding, but planes of dislocation. The dip and strike of these planes have been given to them since Silurian times by the agency of the great earth-movements. In some instance the original structures of the rocks are still recognisable; usually, however, they are wholly obliterated: the old minerals have disappeared as such, and new minerals have been developed, The Eastern Gneissic series has thus no pretension whatever to the title of a sedimentary rock-system. It is a petrological rock-massif, a metamorphic compound, composed of local elements of very different geological ages. In all their essentials these views appear to agree with the farm ore contended and minute results worked out independently, and published by Messrs, Peach and Horne in November 1884.
In the second part of his paper the author gave a summary of the work accomplished among the metamorphic rocks of the Alps and Eastern Germany by Heim and Lehmann; and described the several types of rock-metamorphism found in the Eriboll district, as worked out by himself. The Arnaboll (Hebridean gneiss) can be traced stage by stage from spots where it retains its original strike and petrological characters, to others where it acquires the normal strike and mineralogical features of the ordinary Sutherland schists. The old planes of schistosity become obliterated, and new ones are developed; the original crystals are crushed and spread out, and new secondary minerals, mica and quartz, are developed. The most intense mechanical metamorphism occurs along the grand dislocation (thrust) planes, where the gneisses and pegmatites resting on those planes are crushed, dragged, and ground out into a finely-laminated schist (Mylonite, Gr. mylon, a mill) composed of shattered fragments of the original crystals of the rock set in a cement of secondary quartz, the lamination being defined by minute inosculating lines (fluxion lines) of kaolin or chlorite material and secondary crystals of mica. Whatever rock rests immediately upon the thrust-plane, whether Archæan, igneous, or Palæozoic &c., is similarly treated, the resulting mylonite varying in colour and composition according to the material from which it is formed. The variegated schists which form the transitional zones between the Arnaboll gneiss and Sutherland mica-schists are all essentially mylonites in origin and structure, and appear to have been formed along many dislocation planes, some of which still show between the patches of recognisable Archæan and Palæozoic rocks. These variegated schists (Phyllites or Mylonites) differ locally in composition according to the material from which they have been derived, and in petrological character according to the special physical accidents to which they have been subjected since their date of origin—forming frilled schists, veined schists, glazed schists, &c., &c. The more highly crystalline flaggy mica-schists, &c., which lie generally to the east of the zones of the variegated schists, appear to have been made out of similar material to those of the variegated schists, but to have been formed under somewhat different conditions. They show the fluxion-structure of the mylonites; but the differential motion of the component particles seems to have been the less, while the chemical change was much greater. In some of these crystalline schists (the augen-schists) the larger crystals of the original rock from which the schist was formed, are still individually recognisable, while the new matrix containing them is a secondary crystalline matrix of quartz and mica arranged in the fluxion-planes. While the mylonites may be described as microscopic pressure-breccias with fluxion-structure, in which the interstitial dusty, siliceous, and kaolinitic paste has only crystallized in part; the augen-schists are pressure-breccias, with fluxion-structure in which the whole of the interstitial paste as crystallised out. The mylonites were formed along the thrust-planes, where the two superposed rock-systems moved over each others as solid masses; the augen-schists were probably formed in the more central parts of the moving system, where the all-surrounding weight and pressure forced the rock to yield somewhat like a plastic body. Between these augen-schists there appears to be every gradation, on the one hand, to the mylonites, and on the other to the typical mica-schists composed of quartz and mica. Like the mylonites, the crystalline augenites and micalites present us with local differences in chemical composition (calcareous, hornblendic, quartzose, &c.), suggestive of Archæan, igneous, or Palaeozoic origin. They also show similar structural varieties due to secondary physical changes (frilled, veined, glazed, &c.), as well as others due to the presence of special minerals (garnet, actinolite, &c., &c.).
(yes, I am silly enough to spend the time to type it up, both(!) paragraphs from the photocopy!) I found it odd that the paper describes what the author said, rather than simply saying it, but perhaps this is a summary of a presentation he gave somewhere?
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Date: 2008-04-24 11:24 pm (UTC)--F.
(no subject)
Date: 2008-04-25 12:28 am (UTC)(no subject)
Date: 2008-04-25 05:01 am (UTC)Clicking on that link get a teaser which starts out with:
"Some Results of a Detailed Survey of the Old Coast-Lines near Trondhjem. Norway, by Hugh Miller, F.G. S., H.M. Geological Survey.-During a short visit to Norway in October, 1884, it appeared to the author that the best way to help to a solution of the vexed questions connected with the coast-terracing of Norway was to execute a careful survey of a few square miles of some suitable coast-region upon a sufficiently large scale."
and a notice that one needs to log in or purchase the article if one wants to see it. Alas, UTAS doesn't have on-line access to Nature before the 1990's, so I can't see more of it, but the above snippet doesn't sound as much like a review as the one I typed up yesterday, and it has the same style of ___title____, by __author, alphabet soup, affiliations____, making me wonder if a) they are both reviews, or b) neither of them are, or c) the first is and the second isn't.
I did check and while UTAS does have an intro to geology book that Lapworth wrote, it doesn't have one on the highland controversy. I put in a document delivery request, and let them know that I want it because this article (citation provided) looks like a review, and I want more details from the book, if it exists. Perhaps they will be able to find me a copy. They found the book on Pictish stone carvings in Scotland published in the early 1900's when I asked for it, though in that case it was a more recent facsimile they actually obtained.
(no subject)
Date: 2008-04-25 05:13 am (UTC)